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ICSTI '06, November 26-30 Osaka, Japan
SLAG BEHAVIOUR IN LKAB PELLET AT
ELEVATED TEMPERATURE
It is a important tool in terms of product development
and process research, in addition the risks involved in
full-scale production trials can be avoided.
Nicklas Eklund, Bo Lindblom
[email protected]
LKAB
Technology & Business Development
Svartövägen 16, 974 37 Luleå
SWEDEN
ABSTRACT
Integrated steel plants in Europe operate with mixed
burdens with sinter as major burden constituent and
some plants use only pellet as burden material. It is
important that pellet behaviour is well suited for different
blast furnace burdens.
Therefore it is necessary to
understand pellet behaviour during reduction. As the
raw material costs has increased rapidly during the last
couple of years blast furnace burden materials is an
important area for optimising the economy of the blast
furnace process.
Pellet development at LKAB comprises formulation of
pellet formula and testing in laboratory scale.
The
LKAB Experimental Blast Furnace (EBF) is an excellent
tool to verify experimental pellet behaviour, here
laboratory equipment and EBF-data was used to outline
pellet behaviour at elevated temperature.
Fig. 1 Development route at LKAB
To examine blast furnace burden material in
laboratory enviroment softening and melting equipment
is used. Around the world numerous of different test
set up exists1) with specific characteristics.
At
Studiengesellschaft für Eisenerzaufbereitung (SGA) in
Germany a test method, the REAS test, has been
developed to outline blast furnace burden material
1. INTRODUCTION
during reduction, softening and melting1).
In this
investigation the REAS-test equipment is used to
LKAB is a mining company situated in northern
Scandinavia.
Manufacturing of blast furnace- and
direct reduction pellets and sinter fines is made at three
separate production sites.
Total amount of finished
products is in excess of 20 Mton/year. Development
evaluate LKAB pellets in laboratory enviroment. The
EBF is used when a comparison is made during blast
furnace operation.
2. EXPERIMENT
route at LKAB comprises laboratory scale testing, pilot
scale testing and full scale testing, Fig. 1. The LKAB
EBF is a unique test facility for blast furnace materials.
2.1 Laboratory equipment
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The REAS- test set up has already been described in
receiving hopper. Either a bell or a rotary Top Charger is
detail and will only be discussed breifely here. In Fig.
used to charge the burden material. While using the
1)
2 a schematic view of the REAS-test is shown.
bell system there is a movable armour for distribution
control. Pebbles heaters provides up to 1250 °C in
blast temperature. The blast enter the blast furnace
through one of three tuyeres.
The tuyeres are
separated by 120 degrees and has a diameter of 54 mm
resulting in a blast velocity of 150 m/s at normal blast
volume. One tap hole is used and normal tap to tap
time is one hour. Top gas is transported through the
uptakes and down comers to a dust catcher. Top gas
is further cleaned in a venturi scrubber and a wet
Fig. 2 Schematic view of softening and melting unit
electrostatic precipitator. Finally the top gas is flared in
a torch.
During operation it is possible to collect
Burden material to be tested is mounted in between
material or gas and temperature profiles by inburden
graphite layers and a thermocouple in the burden
probes, Fig. 4. Horisontal probes can be positioned at
material is monitoring increase in temperature. Inlet
five different heights and one inclined probe collect
gas is preheated and outlet gas is analysed to make
material from bosh area.
reduction and reducibility calculations. When sample
measurement give the temperature profile over the
reaches a differential pressure of 200 mmWG gas is
blast furnace height.
A vertical temperature
by-passed to let molten material drip into the cruicible.
Weight change of dripped out material is monitored at
incresing temperature. Furnace is heated electrically
up to 1550 oC and temperature- and gas flow control
during this evaluation is shown in Fig. 3. Hydrogen
and alkali reactions is not simulated in the REAS-test.
Temperature control
Temperature range
20-450 oC
450-900 oC
o
900 C
900-Tmax
Heating rate
5 oC/min
10 oC/min
konstant
5 oC/min
Gas flow control
Gas composition
100 %N2
25%CO/15%CO2/60%N2
35%CO/5%CO2/60%N2
100 %N2
Time
55 min
95 min
until end of test
Fig. 3 Gas- and temperature control of test unit
2.2 The LKAB Experimental Blast Furnace
Fig. 4 The LKAB Experimental Blast Furnace
As to now the experience is that the EBF is a very
sensitive tool for detecting differences in properties for
The LKAB Experimental Blast Furnace has been
different pellet types5-6). The response time is much
described in several publications2-4) and will be briefly
shorter for the EBF compared to a commercial furnace.
outlined here. Burden material are screened at +6 mm
Evaluation of data and comparison to full-scale
for pellet, 6-50 mm for sinter, coke 15-30 mm and fluxes
operation has been described3).
10-20 mm. Iron ore is stored in one of four bins, coke
is stored in a larger bin. A skip transport material to a
3. RESULTS AND DISCUSSION
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Composition of blast furnace burden material that
In addition, the total amount of dripped mass is higher
was tested in the REAS-test and in the EBF is shown in
for the acid pellet grade. From Fig. 8 it is seen that the
Table 1.
amount of primary slag for acid pellet is higher and
attaine in a more narrow temperature interval.
Table 1 Pellet composition of pellet grades
Acid
Fe
66,45
66,51
B2
0,24
0,23
MgO/SiO2
0,78
450
Olivine
400
Dripping mass(g)
Olivine
0,23
Acid
350
300
ACID
250
200
OLIVINE
150
100
50
0
When temperature is increased pellet experience
softening before melting and in the REAS-test softening
240
250
260
270
280
290
300
Time (min)
310
320
330
Fig. 7 Melting behaviour of acid and olivine pellet
Acid pellet show a sharp peak at lower temperature
compared to olivine pellet, Fig. 5.
300
ACID
1500
Temperature (°C)
250
Pressure drop (mmWG)
1600
200
1400
150
1300
100
1200
OLIVINE
50
0
1100
200
220
240
260
Time (min)
280
Dripping mass primary slag (%)
is defined at attained pressure drop of 200 mmWG.
25
Olivine
Acid
20
15
10
5
0
0
10
20
30
40
50
60
70
Temperature interval primary slag (°C)
80
90
Fig. 8 Formation of primary slag of pellets
1000
300
320
During campaign 12 trial with acid and olivine pellets
Fig. 5 Softening behaviour of pellets
were conducted. Blast parameters, injection rate, slag
volume and burden distribuition was kept constant to
The effect of pellet basicity on dripping temperature,
make the evaluation easier. In this study an attempt is
Fig. 6, show higher dripping temperature at increased
made to link the REAS-data with the EBF-data in terms
basicity B3. At lower temperature acid pellet start to
of the high temperature region. Heat loss at tuyere is
drip and the amount of primary slag is higher compared
higher for acid pellet grade, Fig. 9.
to the olivine pellet, Fig. 7.
120
Acid
1360
1340
1320
1280
0,00
0,20
0,40
0,60
0,80
Basicity B3 (CaO+MgO/SiO2)
1,00
1,20
Fig. 6 Effect of pellet basicity on dripping temperature
1550
80
1500
60
1450
40
1400
20
0
1300
Hot metal temperature (°C)
Dripping temperature (°C)
1380
Olivine
Tuyere Heat Loss (kW)
100
1400
1600
OLIVNE
1350
ACID
0
50
100
150
200
250
300
Time (hour)
350
400
450
1300
500
Fig. 9 Development of tuyere heat loss and hot metal
temperature over time
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From operational data burden resistance index is
simulate the softening and melting phenomena of blast
calculated and within each period the permeability is
furnace burden. An attempt is made to link burden
decreasing for increasing heat loss at tuyere, Fig. 10.
behaviour in laboratory softening and melting test to
EBF-data.
Burden Resistance Index
4,5
Based on laboratory tests and results from the EBF it
4,25
R = 0,3775
2
OLIVINE
4
is possible to describe softening and melting behaviour
3,75
of different pellet types during blast furnace operation.
3,5
3
ACID
R 2 = 0,4582
3,25
60
65
70
75
80
85
90
95
100
105
Tuyere Heat Loss (kW)
110
115
120
For evaluation of blast furnace burden material and
125
blast furnace operation research LKAB has an
Fig. 10 Permeability at varying heat level
important tool in the Experimental Blast Furnace.
From the REAS-test it is shown that the acid pellet
soften at lower temperature compared to the olivine
pellet and that the olivine pellet experience better
permeability at higher temperature.
The fayalitic
nature of the primary slag of acid pellet contribute to the
formation of larger amount of primary slag at shorter
temperature interval. With lower softening and melting
temperature of the acid pellet it is expected that the
cohesive zone would be located at a higher position in
the blast furnace compared to the olivine pellet burden.
Results based on excavated material2) from the EBF
confirm the higher cohesive zone position of acid pellet.
REFERENCES
For each pellet grade the burden resistance index is
1)
increasing with increasing heat loss but there is a
difference in level when comparing the two pellet
ICSTI/Ironmaking conf. proc., Toronto, (1998).
2)
grades. Furthermore higher heat losses for the acid
pellet indicate a higher position of the cohesive zone
H. A. Kortmann, V. J. Ritz and K. Koch:
M. Hallin: International BF Lower Zone Symp.,
Wollongong, (2002), 22-1.
3)
L. Hooey, J. Sterneland, M. Hallin: Iron & Steel
and larger burden resistance index for the olivine pellet
Society’s 60th Ironmaking Conference, (2001),
indicate that the cohesive zone is thicker than in the
197.
case of acid pellet.
Also, higher burden resistance
4)
index can be an effect of the surrounding temperature in
the case of olivine pellet with its lower cohesive zone
J. Sterneland, M. Hallin: Proc. 6th Japan-Nordic
Countries Joint Symp., (2000), 9.
5)
L. Sundqvist-Öqvist, A. Dahlstedt, M. Hallin: Iron
& Steel Society’s 60th Ironmaking Conference,
position.
(2001), 167.
4. CONCLUSIONS
6)
L. Hooey, J. Sterneland, M. Hallin: 1st Internat.
Meeting on Ironmaking, Belo Horizonte, Brazil,
The REAS softening and melting test can be used to
(2001).